Brake control valve



June 22, 1937. v E HEwlTT 2,084,684

I BRAKE CONTROL VALVE Filed July 13, 1935 ATTORNEY Q I k L r w INVENTOR 9 ELLIS HEWITT l BY. .9) g g. L R

Patented June 22, 1937 UNITED STATES PATENT OFFICE BRAKE CONTROL VALVE Application July 13, 1935, Serial No. 31,224

14 Claims.

This invention relates to electropneumatic brakes and more particularly to a system in which the brakes may be controlled both electrically and pneumatically.

Braking systems are now in use which employ a brake pipe to supply fluid under pressure to a reservoir from which fluid is supplied to the vehicle brake cylinders to efiect an application of the'brakes. The supply of fluid to the brake cylinder from the reservoir, and the release of fluid from the brake cylinder to the atmosphere is controlled by means of a relay valve which is normally controlled by variations in the pressure of the fluid in a control pipe.

In this system the pressure of the fluid in the control pipe is controlled by means of an engineers brake valve having a pneumatic portion which directly controls the supply and release o1 fluid under pressure to and from the control pipe, and an electric portion which controls the supply and release of fluid under pressure to and from the control pipe through magnet valves.

. in this system a change-over valve is provided which is responsive to the pressure of the fluid in the brake pipe, and which operates on a reduction in the pressure of the fluid in this pipe below a predetermined value to cut oil the control of the relay valve by the control pipe, and to supply fluid under pressure to the relay valve from the reservoir to operate this valve to effect an application of the brakes.

The change-over valve is also operable on an increase in the pressure of the fluid in the brake pipe to cut off the supply of fluid from the reservoir to the relay valve and to restore control of this valve to the control pipe.

In the system heretofore in use a limiting valve has been provided to cut off the flow of fluid to the relay valve from the reservoir when a predetermined pressure is reached, the limiting valve being operative only when the pressure of the fluid in the brake pipe has been reduced so that the change-over valve operates to cut oil control of the relay valve by the control pipe.

The pressure established in the brake cylinder is governed by the pressure of the fluid supplied to the relay valve, and as this valve is controlled by the limiting-valve, the supply of fluid to the brake cylinder is out oii when a predetermined pressure is established therein.

It is the principal object of this invention to provide a braking system of the type described and inv which the change-over valve also serves as a limiting valve when fluid is supplied to the relay valve as a result of operation of the changeover valve in response to a reduction in the pressure of the fluid in the brake pipe.

A further object of this invention is to provide a braking system of the type described in which the change-over valve serves as a limiting valve, and in which means is provided to prevent a release of the brakes by a reduction in the pressure of the fluid in the control pipe during the time that the brakes are applied as a result of operation of the change-over valve in response to a reduction in the pressure of the fluid in the brake pipe.

Another object of the invention is to provide a braking system of the type described having electrically operated valves controlling the supply of fluid under pressure to the control pipe from a reservoir, and the release of fluid from the control pipe together with means subject to the pressure of the fluid in the reservoir and operated on a. predetermined reduction in this pressure to cut off the supply of fluid from the reservoir to the control pipe, whereby the complete loss of pressure in the reservoir, as a result of the faulty operation of the electrically operated valves, or of the supply of fluid to the control pipe, at a time when the control pipe is broken or leaking, will be prevented.

A further object of the invention is to provide an improved braking system.

Other objects of the invention and features of novelty will be apparent from the following description taken in connection with the accompanying drawing, in which Fig. 1 is a diagrammatic view of one form of brake equipment embodying my invention; and

Fig. 2 is a diagrammatic development of the manual control means employed in the system shown in Fig. 1.

As shown in the drawing the electropneumatic brake equipment provided by my invention may comprise a bracket section I, to which is secured a relay valve portion 2, a change-over valve portion 3, an application magnet valve portion 4, and a release magnet valve portion 5.

The relay valve portion 2 may comprise a casing having a piston chamber l 0 containing a piston l5. The chamber at one side of the piston is connected to the control pipe II by way of a passage I2 having a check valve I23 interposed therein which operates to permit fluid to flow from the control pipe to the piston chamber, but to cut off the flow of fluid from the piston chamber to the control pipe. The casing also has a valve chamber I! which is connected to the brake cylinder 20 by Way of the pipe and passage 2|, and which contains a slide valve 22 adapted to be operated by the piston l5 through the medium of a stem 23, and controlling communication between the valve chamber I! and the atmosphere by way of the passage 24'. Fluid also flows from the valve chamber I! to the piston chamber I 0 on the lower side of the piston l5 by way of the passage 25, so that the piston I5 is subject to the opposing pressures of the fluid in the chamber above the piston, and of the fluid in the chamber below the piston, which will be the same as'the pressure of the fluid in the brake cylinder 20.

5 The relay valve portion also includes the chamber 26 which communicates with the reservoir 21 by way of a passage and pipe 28, and this cham ber contains a Valve 3!] normally urged into engagement with a seat rib 3! by means of a spring 34% in order to cut off communication between the chamber 2% and the valve chamber E1. The valve 36 is adapted to be engaged by the end of the piston stem 23 so as to be moved away from the seat rib 3i, and thereby open communication between the chambers IT and 2t and thus permit fluid to flow from the reservoir 2'! to the brake cylinder 2%.

The relay valve portion also has associated therewith a check valve device comprising a valve element 38 normally urged into engagement with a seat rib 39 by means of a spring 40. The chamber 52 within the seat rib 39 is connected to the main reservoir by way of the passage 46 and the brake pipe ll, and the chamber 43 outside of 25 the seat rib 39 is connected by way of the passage E9 to the passage 28 and thereby to the reservoir 2?.

The change-over valve device 3 comprises a casing having a valve chamber 50, which is con- .00 nected to the brake pipe 4? by way of the passage 52 which has a choke 53 interposed therein, and by the passage 3%. The passage 52 also communicates with a pressure chamber 55 by way of a passage 56.

5 The valve chamber 5i? contains a slide valve 57 which is controlled by a stem 58 which has secured thereto the diaphragms St and 6!. The diaphragms 58 and 6I are of unequal diameter, the diaphragm 69 being substantially larger than the diaphragm BI.

The diaphragm to is subject on one side to the pressure of the fluid in the chamber 59 and is subject on the other side to the pressure of the springs 65 and 65.

A stop 6i is provided and engages the end of the stem 58 to limit upward movement of the stem 58, while the end of the stem 58 engages the wall of the valve chamber to limit downward movement of the stem.

The diaphragm 6! is subject on one side to the pressure of the fluid in the valve chamber 5%), and is subject on the other side to the pressure of the fluid in the chamber t8 which communicates by way of the passage 69 with the chamber above the piston of the relay valve device.

The stem 58, therefore, is moved upwardly by the pressure of the fluid in the valve chamber 50 acting on the lower face of the diaphragm 6t! and by the pressure of the fluid in the chamber 68 60 acting on the lower face of the diaphragm fi l, and is urged downwardly by the pressure of the fluid in the valve chamber 58 acting upon the upper side of the diaphragm SI, and by the springs 64 and 55.

65 The slide valve 57 has a port It formed therein and controlling communication between the passage ll, which communicates with the control passage I2 on the side of the check valve I3 remote from the relay valve device, and the pas- 7 sage l2 which communicates by way of the passage $9 with the chamber above the piston of the relay valve device. The slide valve 5'! also controls communication between the passage I5, which communicates with the reservoir 2"! by way 7 of the passage 49, and the passage I2 which com- 'municates with the chamber above the piston of the relay valve device.

The port 18 in the valve 51 is arranged so that when the stem 58 is in the upper position, communication is established between the passages II and I2 and communication is cut off between the passages and I2, while in the lower position of the stem 58, communication is cut off between the passages "II and i2, and is established between the passages I5 and I2. The port it is also arranged so that in an intermediate position of the stem 58 communication is cut off between passage I2 and both of the passages II and I5. This is the lap position of the change-over valve device.

This equipment has a limiting valve associated therewith and comprises a pair of casing sections 8!} and BI having a diaphragm 82 secured therebetween. The diaphragm 82 is subject on one side to the pressure of the fluid in the chamber 83, which communicates by way of the pipe and passage 84 with the passage 28 and thereby with the reservoir El, and is subject on the other side to a spring 85. The diaphragm 82 controls the operation of the valve 8? which is urged to the unseated position by a spring 88, and which controls communication between chamber 83 and the chamber 89, which is connected by way of the pipe and passage 99 with the chamber 9! in the application magnet valve device t.

The application magnet valve device t comprises a casing having a chamber SI therein in which is mounted a valve element 93 which is held in engagement with a seat rib 95 by means of a spring 96 and by the pressure of the fluid in the chamber 97 on the upper side of the valve element 93.

The valve element 93 is urged to the unseated position by the pressure of the fluid acting on the valve element outwardly of seat rib 95. The valve element 93 controls communication between the chamber Qi and the chamber 9% which is connected through a restricted passage It?! to a passage IM which communicates with the control pipe passage I2.

The application magnet valve device also includes a casing section having a chamber I05 formed therein in which is mounted a double beat valve element H36 which controls communication between the chamber I 05 and the chamber Hill, which is in constant communication with the chamber M by way of a passage I68, and also controls communication between the chamber I65 and the atmosphere by way of the passage I09. cation with the chamber 9? by way of the passage II@. The double beat valve element I06 is normally urged to its upper seated position by means of the spring HI, and on energization of the winding of the magnet valve device the valve element is moved to its lower seated position.

The release magnet valve device 5 comprises a casing having a chamber I 29 therein which communicates by way of a passage I2I with the control pipe passage I2, and which has mounted therein a valve element I22 which is normally urged into engagement with a seat rib I23 by means of a spring IN and by the pressure of the fluid in the chamber I25 on the upper side of the valve element I22. The valve element 622 is urged upwardly by the pressure of the fluid in the chamber I20 acting on the valve 822 outwardly of the seat rib I23. The valve element l 22 controls communication between the chamber I'M and the chamber E24, which is in communica- The chamber m5 is in constant communi- 1 tion with the atmosphere by way of a choke or restricted passage I28 and the passage I26.

The release magnet valve device 5 also includes a casing section having a chamber I39 formed therein, in which is mounted a double beat valve element I 3| and which is in constant communication with the chamber M5 by way of a passage I32. This casing section also has a chamber I33 therein which is in constant communication with the chamber I25 by way of a passage I34. The double beat valve element I3I controls communication between the chamber I33 and the chamber I30, and between the chamber I30 and the atmosphere by way of the passage I31. The valve element I3I is normally urged to its upper seated position by means of a spring I39, and is moved to its lower seated position upon energization or" the winding of the release magnet valve device.

The brake pipe 41 has a foot valve device I53 interposed therein and comprising a casing having a chamber i5I formed therein which is in constant communication with the main reservoir 45, and a chamber I52 which is in constant communication with the brake pipe 41. Communication between the chamber I5! and the chamber I52 is controlled by means of the valve element I53 which is urged to its seated position by means of a. spring B54.

The casing of the foot valve device I59 also has a chamber I55 formed therein which is in constant communication with the atmosphere by way of the passage I55.

Communication between the chamber I52 and the chamber I55 is controlled by a diaphragm I51 which is-engageable with a seat rib I53. Movement of the diaphragm I51 is controlled by the foot pedal I59 acting through a stem I55. The foot pedal I59 is normally urge-d out of engagement with the stem I55 by means of a spring IBI, but on the application of pressure to the foot pedal I59 the stem I60 forces the diaphragm I51 into engagement with the seat rib I58 to cut off communication between the chamber I52 and the chamber I55, and to move the valve element I53 to the unseated position against the pressure of the spring I54, and thereby permit fluid to flow from the main reservoir through the chamber I 5! to the chamber I52 and therefrom to the pipe 41.

On the release of pressure from the foot pedal I59 the diaphragm I51 is moved to the right, as viewed in the drawing, due to the pressure of the spring I54 transmitted through the valve element I53 and to the pressure of the fluid within the seat rib I58. This permits the valve I53 to move to its seated position to cut oil the flow of fluid from the main reservoir 45 and to permit the fluid in the brake pipe 41 to escape to the atmosphere by way of the chamber I52, the chamber I55 and the passage I55.

For controlling the brakes a combined brake switch and brake valve device IE2 is provided and may comprise a pneumatic portion I63 for controlling the pressure of the fluid in the control pipe in the usual manner, and an electric portion I64 for controlling the pressure of the fluid in the control pipe by electrically controlled means.

The pneumatic portion of the combined brake switch and brake Valve device I52 comprises a rotary valve operated by the handle 155 and controlling communication between the supply pipe I66, which communicates with the main reservoir 45, and the control pipe II, being adapted in. one position of the handle I65 to permit fluid to flow from the main reservoir by way of the pipe I 66 to the control pipe I i. The rotary valve also includes means operable in another position of the handle I55 to connect the control pipe I I with the exhaust passage I61 so that fluid under pressure in the control pipe I! is released to the atmosphere, and in still another position of the handle I65, the rotary valve cuts off communication between the supply pipe I65 and the control pipe II and between the control pipe II and the exhaust passage I61.

The electric portion I54 of the combined brake switch and brake valve device may comprise a movable drum H5 on which is mounted contacts HI and I12 which are electrically connected together by means of a wire I14, and which are adapted to engage at different times the contacts I15, 511 and I13 for electrically controlling the operation of the brakes.

The contact I16 is connected by means of a suitable conductor to a suitable source of power, such as a battery I85, the other terminal of which is connected to ground. The contact I11 is con nected by means of a wire M2 to one terminal of the winding of the application magnet valve i, the other terminal of which is connected to the ground. The contact I18 is connected by means of a wire I84 with one terminal of the winding of the release magnet valve 5, the other terminal of which is connected to the ground.

In operation, assuming that the main reservoir 45 is charged with fluid under pressure to a pre determined pressure, and that the operator presses upon the pedal I59 of the foot valve device I55 so as to establish communication through the brake pipe 41, fluid under pressure will be supplied by way of the brake pipe 111 to the passage 46 to move the check valve 38 to the unseated position and fluid will then flow past the valve 38 to the passage 49, and therefrom to the passage 28 which communicates with the reservoir 2?. Fluid under pressure also flows from the brake pipe 41 through the choke 53 to the passage 52 and therefrom to the valve chamber 55 in the change-over valve device, and also by way of the passage 55 to the pressure chamber 55.

When a predetermined pressure is established in the valve chamber 55, fluid under pressure acting on' the diaphra .1 55 urges the stem 58 upwardly into engagement with the stop 51, thereby moving the valve 51 to a position to establish communication between the passages it and 12.

Fluid supplied past the check valve 38 to the passage 28 also flows by way of the passage and pipe 84 to the chamber 83 of the limiting valve device, and on an increase in the pressure of the fluid in this chamber to a predetermined value the diaphra m 82 is moved upwardly against the spring 85, thereby permitting the spring 88 to move the valve 87 away from its seat. Fluid may thereupon flow from the chamber 83 to the chamber 89 and thence by way of the pipe and passage to the chamber iii in the application magnet valve device i. Fluid supplied to the chamber 99 flows by way of the passage I68 to the chamber I51 and past the unseated valve I06 to the chamber 91 on the spring side of the valve 93 so that the valve 53 is held in engagement with the seat rib thereby preventing the supply of fluid to the chamber 39 and to the control pipe I2.

Assuming that the brake valve handle IE5 is in the release position fluid under pressure will be released from the control pipe it through the port in the rotary valve in the pneumatic section of the combined brake switch and brake valve, and at the same time the contact @712 on the drum ill of the switch portion of the combined brake switch and brake valve will engage the contact H8 and thereby complete a. circuit through the winding of the release magnet valve device 5.

When the winding of this magnet valve device is energized the valve element l3l is forced downwardly against the pressure of the spring i559, thereby cutting ofl the flow of fluid from the chamber 533 to the chamber its on the upper side of the valve element E22, and permitting the fluid in the chamber 525 to escape by way of the passage 832, the chamber 538 and the release passage til. When fluid is vented from the chamber WE the valve element i252 is forced upwardly by the pressure of the fluid in the chamber iZS acting on the portion of the valve element outside of the seat rib E23, thereby opening communication between the chamber we and the atmosphere by way of the chamber l2 i, the restricted passage i2'i5 and the passage I26. Fluid, therefore, is released from the corn trol pipe it both by way of the release magnet valve device, and by way of the pneumatic portion of the brake controlling valve.

When it is desired to apply the brakes the handle 5355 of the combined brake switch and brake valve device is moved to the application position, and the ports in the rotary valve in the pneumatic section 563 of the combined brake switch and brake valve device establish communioation between the pipe which leads from the main reservoir 35, and the control pipe II so that fluid under pressure is supplied to the control pipe. At the same time the contact Ill engages the contact I'i'l so as to complete a circuitthrough the winding of the application magnet valve device l, while the contact H2 is moved out of engagement with. the contact US so that the circuit through the winding of the release magnet valve device is interrupted.

When the circuit through the winding of the application magnet valve device is completed the valve element 536 is moved downwardly against the spring ill to its lower seated position, thereby cutting off the supply of fluid under pressure from the chamber id? to the chamber 9? on the upper side of the valve element 93. At the same time the fluid under pressure in the chamber Si is released to the atmosphere by way of the passage i539. When the fluid is released from the chamber or the valve element 93 is moved upwardly by the pressure of the fluid in the chamber 9! acting on the valve outwardly of the seat rib 55, and fluid under pressure then flows from the reservoir 2?! by way of the pipe and passage 23, passage 86, the limiting valve device and the passage fill to the chamber 99, and therefrom through the restricted communication lilEfl to the passage Ill! and then to the control passage 92.

The fluid which is supplied to the control passage I2 flows past the check valve l3, and then to the chamber above the piston of the relay valve device.

Fluid supplied to the control passage lit by the application magnet valve device t, or by the pneumatic portion of. the engineers brake valve device, flows by way of the passage i2i to the chamber H20 of the release magnet valve device 5. Fluid supplied to the chamber i223 flows therefrom by way of the passage lii l to the chamber I 33. As the winding of the release magnet valve device is deenergized at this time the double beat valve I M is held in the upper seated position by the spring H59, and fluid supplied to the charm her 533 may flow past the valve iii to the chamber I39 and therefrom by way of the passage M2 to the chamber I 25 on the spring side of the valve I22 where it acts upon the valve 525? to hold it in engagement with the seat rib ass and thereby prevent the release of fluid from the control passage I2.

The pressure of the fluid in the chamber of the relay valve device on the upper side of the piston I5 forces the piston downwardly with the result that the slide valve 22 cuts off the exhaust communication is, and the end of the stem 23 engages the valve 3% so that the valve moved downwardly against the spring 3 When the valve 30 is unseated fluid under pressure flows from the reservoir 2? by way of the pipe and passage 28 to the chamber 26, and then to the chamber ll, and therefrom by way of the pass-age and pipe M to the brake cylinder 2% to efieet an application of the brakes.

At the same time fluid under pressure in the chamber ll flows by way of the passage 25 to the chamber on the lower side of the piston it, and when the pressure of the fluid in this portion of the chamber builds up to the same value as the pressure of the fluid in the chamber above the piston E5, the piston will be moved upwardly so as to permit the valve 353 to seat on the seat rib 3! and thereby cut oil the further flow of fluid under pressure from the reservoir to the brake cylinder.

II" the pressure of the fluid in the chamber ii, and hence in the chamber on thelower face of the piston to, exceeds the pressure of the fluid in the chamber above the piston l5 the piston will move upwardly until the slide valve 22 on covers the exhaust port 2d. Fluid will then be released until the pressure of the fluid in the brake cylinder is reduced to the same value as the pressure of the fluid in the chamber above the piston l5, which is the pressure of the fluid in the control pipe, at which time the piston IE will move downwardly so that the valve 22 laps the exhaust passage 24.

It will be seen, therefore, that the relay valve operates to control the pressure of the fluid in the brake cylinder in response to the variations in the pressure in the control pipe ii, and to maintain the pressure of the fluid in the brake cylinder substantially the same as that in the control pipe.

When the desired degree of application of the brakes has been secured the handle E55 of the combined brake switch and brake valve is moved to the lap position, in which positlon the windings of both the application magnet valve device and the release magnet valve device are deenergised, while the pneumatic portion of the combined brake switch and brake valve operates to out off the supply of fluid from the main reservoir to the control pipe, and to cut oil the release of fluid from the control pipe to the atmosphere.

As a result of movement or" the handle we of the combined brake switch and brake valve to the lap position the pressure of the fluid in the control pipe II is maintained, and the relay valve device operates to maintain the pressure in the brake cylinder at substantially the same value.

If at this time it is desired to increase the degree of application of the brakes the handle I65 of the combined brake switch and brake valve is moved to the application position, in which position the winding of the application magnet valve device 4 is energized, thereby effecting the supply of fluid under pressure to the control passage I2 by way of the application magnet valve device, and at the same time the rotary valve in the pneumatic portion of the combined brake switch and brake valve is moved to a position to supply fluid under pressure to the control pipe II from the main reservoir 45 by way of the pipe I66. When the pressure of the fluid in the passage [2 is increased the pressure of the fluid in the chamber above the piston of the relay valve is similarly increased, and the relay valve operates to produce a similar increase in the pressure of the fluid in the brake cylinder.

If it is desired to release the brakes the handle I of the combined brake switch and brake valve is moved to the release position, in which position the contact I12 engages the contact I18 to complete a circuit through the winding of the release magnet valve device 5, and thereby efiect the release of fluid under pressure from the control pipe passage I2, while the rotary valve in the pneumatic portion of the combined brake switch and brake valve is moved to a position to release fluid from the control pipe II to the atmosphere by way of the atmospheric exhaust passage I61.

When fluid is released from the control pipe I I and the passage I2, fluid is also released from the chamber in the relay valve device above the piston I5, assuming that the change-over valve device has remained in the position in which it is shown in Fig. l of the drawing, and on a reduction in the pressure of the fluid in the chamber above the piston of the relay valve device, this valve operates to reduce the pressure in the brake cylinder a similar amount. I

If during the operation of the system the pressure of the fluid in the brake pipe 41 is reduced below a predetermined value as a result of the release of pressure on the pedal I59 of the foot valve device I50, either intentionally or otherwise, or if the pressure of the fluid in this pipe is reduced as a result of the parting of the cars in a train, the pressure of the fluid in the passage 52, and in the valve chamber 50 of the change-over valve device will be reduced, while the check valve 38 will prevent the release of fluid from the reservoir 21 to the atmosphere.

When the pressure of the fluid in the valve chamber 56 of the change-over valve portion is reduced below a predetermined value, the stem 58 is urged downwardly by the springs 64 and 65, and the slide valve 51 is moved to a position in which communication is cut off between the passages TI and I2, and in which communication is established between the passage I5 and the passage I2, with the result that fluid under pressure is supplied from the reservoir 21 by way of the pipe and passage 28, the passage 49 and the passage I5 to the port Ill in the slide valve 51, and therefrom to the passage 12, which connects with the passage 69 leading to the chamber above the piston in the relay valve device and which by-passes the check valve I 3. At the same time fluid flows by way of the passage 69 to the chamber 68 on the lower side of the diaphragm to the lap position, in which position the passage 12 is cut off from both the passages II and I5.

As a result of the supply of fluid under pressure to the chamber in the relay valve device above the piston I5 this valve operates to supply fluid under pressure to the brake cylinder 29 from the reservoir 2'! until the pressure of the fluid in the brake cylinder equals that in the chamber of the relay valve device, which will be the same as that in the chamber 68 of the change-over valve portion. This insures that in the event of loss of pressure in the brake pipe 4'! the brakes will be automatically applied to a predetermined degree.

When the slide valve 51 of the change-over valve portion is in its lower position, that is in the position in which communication is established between the passage 15 and the passage I2, or is in the lap position, in which position the passage ?Z is out 01f from both the passages H and I5, the release of fluid from the control pipe II and the passage I2 associated therewith is ineffective to release fluid from the chamber above the piston of the relay valve as the check valve I3 cuts off communication through the passage I2, and the change-over valve cuts off communication by way of the by-pass passage 69. Therefore, until the pressure of the fluid in the brake pipe 41 is increased to a predetermined high value sufiicient to force the stem 58 of the changeover valve to move to its upper position so that the port Ill in the slide valve 51 again establishes communication between the passages "II and H, the brakes will be held applied, and cannot be released. As soon, however, as the pressure of the fluid in the brake pipe 41 is reestablished, the op erator will again have normal control of the brake system, and can release the brakes by releasing the pressure in the control pipe II.

It will be seen, therefore, that the change-over valve portion operates not only to change the system over from normal control by the operator, at which time the operator can regulate the application and release of the brakes by varying the pressure of the fluid in the control pipe, to a condition in which the brakes are automatically applied by fluid under pressure supplied from the reservoir on the vehicle, but that this valve portion also operates to regulate the degree of pressure established in the brake cylinder when the brakes are applied as a result of movement of the change-over valve device to the latter position.

The system provided by this invention includes the limiting valve device which is interposed in the passage between the reservoir 21 and the application magnet valve device 4.

If for any reason one of the magnet valve devices should be rendered inoperative and stick in an open position, and at the same time the fluid in the control pipe I I were released, either intentionally or otherwise, all of the fluid under pressure in the reservoir 2'! would escape to the atmosphere by way of the control pipe II. The limiting valve device operates to prevent this occurrence.

The limiting valve includes the valve element 8! controlled by the diaphragm 82, and when the pressure of the fluid in the chamber 83, which is in constant communication with the reservoir 21, falls to a predetermined low value the spring 85 presses the diaphragm downwardly and moves the valve element 81 to its closed position, thereby shutting off the flow of fluid from the reservoir to the application magnet valve device and therefrom to the control pipe II.

The limiting valve device, therefore, operates to shut off the flow of fluid from the reservoir 2? to the control pipe II in the event that the pressure of the fluid in the reservoir 2? falls below a predetermined low value. This prevents the complete loss of fluid from the reservoir 21 by way of the control pipe II.

After operation of the limiting valve to out off the supply of fluid under pressure to the control pipe by means of the application magnet valve, the operator is able to effect an application of the brakes by means of the pneumatic portion of the engineers brake valve which may be operated to supply fluid to the control pipe and thereby to the relay valve device to effect the application of the brakes.

If the operator is unable to effect an application of the brakes by supplying fluid to the control pipe by operation of the engineers brake valve, he may effect an application of the brakes by releasing pressure from the foot pedal 559, which results in the release of fluid from the brake pipe 41, and on a reduction in the pressure inthispipe,the ch'ange-overvalve device 3 operates to supply fluid to the relay valve device and thereby produce an application of the brakes.

While a preferred embodiment of brake system provided by my invention has been illustrated and described in detail, it should be understood that the invention is not limited to these details of construction and that numerous changes and modifications may be made without departing from the scope of the following claims.

Having now described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. In a braking system, a brake cylinder, a reservoir, a brake pipe, means for supplying fluid under pressure to the brake pipe, means for supplying fluid under pressure to the reservoir,

a relay valve device controlling the flow of fluid from the reservoir to the brake cylinder, the relay valve device comprising a movable abutment subject on one side to the pressure of the fluid in a chamber in the valve device, and valve means responsive at all times to the pressure of the fluid in the relay valve device chamber and in the brake pipe for controlling the flow of fluid from the reservoir to the chamber in the relay valve device.

2. In a braking system, a brake cylinder, a reservoir, a brake pipe, means for supplying fluid under pressure to the brake pipe, means for supplying fluid under pressure to the reservoir, a relay valve device comprising a valve element controlling the flow of fluid from the reservoir to the brake cylinder and controlled by means subject to the opposing pressures of the fluid in the brake cylinder and of the fluid in a chamber in the relay valve device, and valve means responsive at all times to the pressure of the fluid in the relay valve device chamber and in the brake pipe for controlling the flow of fluid from the reservoir to the chamber in the relay valve device.

3. In a braking system, a brake cylinder, a reservoir, a brake pipe, means for supplying fluid under pressure to the brake pipe, means for supplying fluid under pressure to the reservoir, a relay valve device controlling the flow of fluid from the reservoir to the brake cylinder, the relay valve device comprising an abutment subject to the pressure of the fluid in a chamber in said relay valve device, a control pipe communicating with said relay valve chamber, a check valve in the passage between the control pipe and the relay valve chamber and operable to permit fluid to flow from the control pipe to the relay valve chamber and to cut off the flow of fluid from the relay valve chamber to the control pipe, a passage communicating with the relay valve chamber and with the control pipe and by-passing the check valve, and valve means controlling communication through said by-pass passage.

4. In a braking system, a brake cylinder, a reservoir, a brake pipe, means for supplying fluid under pressure to the brake pipe, means for supplying fluid under pressure to the reservoir, a relay valve device controlling the flow of fluid from the reservoir to the brake cylinder, the relay valve device comprising an abutment subject to the pressure of the fluid in a chamber in said relay valve device, a control pipe communicating with said relay valve chamber, a check valve in the passage between the control pipe and the relay valve chamber and operable to permit fluid to flow from the control pipe to the relay valve chamber and to cut oif the flow of fluid from the relay valve chamber to the control pipe, a passage communicating with the relay valve chamber and with the control pipe and joy-passing the check valve, and valve means responsive to the pressure of the fluid in the relay valve device chamber for controlling communication through said by-pass passage.

5. In a braking system, a brake cylinder, a reservoir, a brake pipe, means for supplying fluid under pressure to the brake pipe, means for supplying fluid under pressure to the reservoir, a relay valve device controlling the flow of fluid from the reservoir to the brake cylinder, the relay valve device comprising an abutment subject to the pressure of the fluid in a chamber in said relay valve device, a control pipe communicating with said relay valve chamber, a check valve in the passage between the control pipe and the relay valve chamber and operable to permit fluid to flow from the control pipe to the relay valve chamber and to cut off the flow of fluid from the relay valve chamber to the control pipe, a passage cornrnunicating with the relay valve chamber and with the control pipe and by-passing the check valve, and valve means responsive to the pressure of the fluid in the brake pipe for controlling communication through said by-pass passage.

6. In a braking system, a brake cylinder, a reservoir, a brake pipe, means for supplying fluid under pressure to the brake pipe, means for supplying fluid under pressure to the reservoir,arelay valve device controlling the flow of fluid from the reservoir to the brake cylinder, the relay valve device comprising an abutment subject to the pressure of the fluid in a chamber in said relay valve device, a control pipe communicating with said relay valve chamber, a check valve in the passage between the control pipe and the relay valve chamber and operable to permit fluid to flow from the control pipe to the relay valve chamber and to cut off the flow of fluid from the relay valve chamber to the control pipe, a passage communicating with the relay valve chamber and with the control pipe and by-passing the check valve, and valve means responsive to the pressure of the fluid in the relay valve chamber for controlling the flow of fluid from the reservoir to the relay valve device chamber and controlling communication through said by-pass passage.

7. In a braking system, a brake cylinder, a reservoir, a brake pipe, means for supplying fluid under pressure to the brake pipe, means for supplying fluid under pressure to the reservoir, a relay valve device controlling the flow of fluid from the reservoir to the brake cylinder, the relay valve device comprising an abutment subject to the pressure of the fluid in a chamber in said relay valve device, a control pipe communicating with said relay valve chamber, a check valve in the passage between the control pipe and the relay valve chamber and operable topermit fluid to flow from the control pipe to the relay valve chamber and to cut on" the flow of fluid from the relay valve chamber to the control pipe, a passage communicating with the relay valve chamber and with the control pipe and by-passing the check valve, and valve means responsive to the pressure of the fluid in the relay valve device chamber and to the pressure of the fluid in the brake pipe for controlling communication through said by-pass passage.

8. In a braking system, a brake cylinder, a reservoir, a brake pipe, means for supplying fluid under pressure to the brake pipe, means for supplying fluid under pressure to the reservoir, a

relay valve device controlling the flow of fluid from the reservoir to the brake cylinder, the relay valve device comprising an abutment subject to the pressure of the fluid in a chamber in said relay valve device, a control pipe communicating with said relay valve chamber, a check valve in the passage between the control pipe and the relay valve chamber and operable to permit fluid to flow from the control pipe to the relay valve chamber and to cut off the flow of fluid from the relay valve chamber to the control pipe, a passage communicating with the relay valve chamber and with the control pipe and by-passing the check valve, and valve means responsive to the pressure of the fluid in the brake pipe for controlling the flow of fluid from the reservoir to the relay valve device chamber and controlling communication through said by-pass passage.

9. In a braking system, a brake cylinder, a reservoir, a brake pipe, means for supplying fluid under pressure to the brake pipe, means for supplying fluid under pressure to the reservoir, a relay valve device controlling the flow of fluid from the reservoir to the brake cylinder, the relay valve device comprising an abutment subject to the pressure of the fluid in a chamber in said relay valve device, a control pipe communicating with said relay valve chamber, a check valve in the passage between the control pipe and the relay valve chamber and operable to permit fluid to flow from the control pipe to the relay valve chamber and to out Oh the flow of fluid from the relay valve chamber to the control pipe, a passage communicating with the relay valve chamber and with the control pipe and by-passing the check valve, and valve means responsive to the pressure ofvfluid in the relay valve chamber and to the pressure of fluid in the brake pipe for controlling the flow of fluid from the reservoir to the relay valve device chamber and controlling communication through said by-pass passage.

10. In a braking system, in combination, a brake cylinder, a brake pipe, a relay valve device operated by an increase in fluid pressure in a chamber therein for supplying fluid under pressure to the brake cylinder, and a valve device subject to and operated upon a reduction in brake pipe pressure for supplying fluid under pressure to said relay valve device and subject at all times to and operated by a predetermined increase in the pressure of fluid supplied to said relay valve device chamber for cutting oii the supply of fluid under pressure to said relay valve device.

11. In a braking system, in combination, a brake cylinder, a brake pipe, a relay valve device operated by an increase in fluid pressure in a chamber therein for supplying fluid under pressure to the brake cylinder, and valve means comprising a valve for controlling the supply of fluid under pressure to said relay valve device chamber and movable abutments for operating said valve, one of said abutments being subject to brake pipe pressure and the other abutment being subject at all times to the pressure of fluid supplied to said relay valve device by said valve means.

12. In a braking system, a brake cylinder, a reservoir, a brake pipe, means for supplying fluid under pressure to the brake pipe, means for supplying fluid under pressure to the reservoir, a relay valve device operated by an increase in fluid pressure for supplying fluid under pressure from said reservoir to the brake cylinder, valve means subject to and operated upon a reduction in brake pipe pressure for supplying fluid under pressure to the relay valve device, and subject to and operated by a predetermined increase in the pressure of fluid supplied to said relay valve device for cutting off the supply of fluid under pressure to said relay valve device, electrically controlled valve means for supplying fluid under pressure to the relay valve device from said reservoir, and means subject to and operated upon a reduction in the pressure of the fluid in the reservoir for cutting oh? the supply of fluid from the reservoir to the relay valve device by said electrically controlled valve means.

13. In a braking system, in combination, a brake pipe, a brake cylinder, a reservoir, a relay valve device operated by an increase in fluid pressure for supplying fluid under pressure from the reservoir to the brake cylinder, a valve device subject to and operated upon a reduction in brake pipe pressure for supplying fluid under pressure to said relay valve device, and subject to and operated by a predetermined increase in the pressure of fluid supplied to said relay valve device for cutting ed the supply of fluid under pressure to the relay valve device, electrically controlled valve means for supplying fluid under pressure from the reservoir to the relay valve device, and means subject to and operated by a predetermined reduction in the pressure of the fluid in said reservoir for cutting off the supply of fluid from the reservoir to the relay valve device by said electrically controlled valve means.

i l. In a braking system, in combination, a brake cylinder, a brake pipe, a reservoir, a relay valve device operated by an increase in fluid pressure for supplying fluid under pressure from the reservoir to the brake cylinder, and a valve device subject to and operated upon a reduction in brake pipe pressure for supplying fluid under pressure from the reservoir to the relay valve device, and subject to and operated by a predetermined increase in the pressure of the fluid supplied to the relay valve device by said valve device for cutting oiT the supply of fluid under pressure from said reservoir to the relay valve device.

ELLIS E. HEWITT. 

